This invention relates in general to devices for testing gases and in particular to a new and useful colorimetric gas dosimeter comprising longitudinally elongated transparent element subdivided into a plurality of chambers extending along its longitudinal axis.
The invention concerns a colorimetric gas dosimeter, which contains a granular indicator substance in a closed, transparent, hollow unit that can be opened on one side.
A gas dosimeter of this type is described in German OS No. 14 98 909. The known dosimeter is a glass tube filled with a granular indicator material, which can be opened on one side to allow gas to diffuse from there through the interior of the glass tube and that the hazardous substance to be detected causes a discoloration in the indicator material. The zone of discoloration extends along the dosimeter tube with the continued diffusion of the hazardous substance into the indicator material. The indicating sensitivity of the known gas dosimeters depends mainly on the ratio of the effective diffusion cross section to the surface of the cross section of the indicator layer. Small amounts of gaseous hazardous substances to be detected result in a weaker discoloration of the still unchanged color of the indicator as the zone of discoloration progresses. The reason for this is found in the fact that the hazardous substance molecules, permeating the indicator at the opening must traverse an ever extending zone of discoloration before they reach the interphase of the indicator between the zone of discoloration and the unchanged zone, to enter into a chemical reaction of discoloration with the indicator there. During the traversing of the indicator zone already changed in color, the molecules of hazardous substance newly diffusing into the gas dosimeter are hindered in their diffusion to the indicator layer still unchanged in color by the packing of the spent granular indicator material. The diffusion cross section for the molecules of hazardous substance newly entering the opening is thereby considerably decreased. Consequently, the known gas dosimeters are not suitable with low concentrations of hazardous substances for an early detection of hazardous doses since the amount of indicator offered in the first layers attracts the diffusion molecules of hazardous substances by chemisorption within an insignificant length, in comparison with the total length of the indicator, making the resulting zone of discoloraion inaccessible for a quantitative evaluation.